(kən-glŏm'ə-rāt') A coarse-grained sedimentary rock consisting of round rock fragments cemented together by hardened silt, clay, calcium carbonate, or a similar material. The fragments (known as clasts) have a diameter of at least 2 mm (0.08 inches), vary in composition and origin, and may include pebbles, cobbles, boulders, or fossilized seashells. Conglomerates often form through the transportation and deposition of sediments by streams, alluvial fans, and glaciers.